1. Field of Invention
The present invention relates to a method of depositing silicon nitride. More particularly, the present invention relates to a method of increasing selectivity in silicon nitride deposition.
2. Description of Related Art
Silicon nitride is a dielectric material commonly used in semiconductor fabrication. Silicon nitride layer mainly serves as an etching mask for etching silicon oxide layer. In addition, because silicon nitride is a barrier for the diffusion of oxygen, the mask layer can also serve as a barrier for preventing oxidation of the active region of a silicon chip. Aside from these advantages, silicon nitride layer is also highly resistant to moisture penetration. Consequently, a silicon nitride layer is often used as a protective passivation layer over semiconductor devices. Because silicon nitride has so many useful applications, the process of forming silicon nitride layer over silicon chip is an important step.
At present, the reacting conditions for the formation of a silicon nitride layer over a silicon oxide layer and a substrate surface are such that thickness over each of the layers are almost identical. However, following the progress in semiconductor manufacturing technologies, process simplification is very important. The conventional method of forming silicon nitride layer cannot produce silicon nitride layer with different thickness over different type of surfaces in a single deposition step.
Accordingly, one object of the present invention is to provide a method of increasing selectivity in silicon nitride deposition. In other words, the ratio between the thickness of the silicon nitride layer formed over a silicon oxide layer and the thickness of the silicon nitride layer formed over a substrate surface in the same process is increased.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of increasing the selectivity of silicon nitride deposition. First, a substrate is provided. A silicon oxide layer is formed over a portion of the substrate. Ammonia NH3 is passed over the silicon oxide layer and the substrate surface for a definite period to perform a surface treatment. Thereafter, silicon nitride is deposited over the substrate and the silicon oxide layer.
In this invention, a nitrogen-containing gas, preferably ammonia NH3, is used to perform a surface treatment of the substrate surface and the silicon oxide surface. After the surface treatment, a single deposition step can be used to deposit silicon nitride to a different thickness over the silicon oxide layer and the substrate. Since there is no need to perform separate deposition steps to form a silicon nitride layer over the silicon oxide layer and the substrate, manufacturing is simplified.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.